The researchers from Belgium and the United States found that half of the gains made by creating new forests have been undermined by importing forest products from neighbouring countries that don't protect their environment.

In Vietnam, for example, stronger domestic conservation policies have encouraged farmers to regrow forests on the marginal areas of their land. But as a result, some of the timber products Vietnam once produced itself must now be imported from other countries

"This illustrates the diabolical problem of leakage, and the ever present danger of unintended consequences which we come upon time and again," says Dr Andrew Reeson, an economist from CSIRO Ecosystem Services.

"When you make changes in one country, in this case reforestation, it is going to lead to flow-on impacts elsewhere. Here they have found a loss of around 50% of the forestation benefits in one country simply by shifting the deforestation abroad."

The authors of the study point out that forest leakage is not a new phenomenon. The extensive forests which grow in Europe and in parts of the United States today have survived because these countries imported large amounts of timber from South America and Africa in the 19th and 20th centuries.

Lead author Dr Patrick Meyfroidt of Université Catholique de Louvain in Belgium, says national policies should 'take care' to reduce the risks of leakage, and that environmental degradation should be accounted for in international trade.

Environmental economist Dr Paulo Santos says the paper is an honest work, but he says it's cynical to expect people to look after the forests without being paid for it.

"Trying to prevent leakage through global agreements and certification requires a huge amount of money and there will always be some country that will find it in its best interests to just evade that kind of regulation.

"The paper is suggesting that preventing leakage with 100% certainty is completely needed. It's a nice idea but nothing is going to get done in the next 10 years, probably.

"You'll have to accept some leakage and eventually extend the payment to those countries. You have to make the whole system interesting for everyone."

According to Reeson, Australia's future forest policies could be informed by the new research.

"It shows how decisions that we make in Australia, such reducing timber harvests, would have flow-on impacts elsewhere in the world," he says.

"If Australia were to change its forest policy we would need to think not just about what that would do to Australian forests but how that's going to flow through global trade to forests in Indonesia and elsewhere."

Santos says the issue is likely to be raised when delegates meet at the Conference of the Parties to the Framework Convention on Climate Change (UNFCCC) in Mexico at the end of the month.

The Reducing Emissions from Deforestation and Degradation (REDD) scheme, which offers financial incentives to poor countries to stop deforestation, was seen by many as one of the few successful outcomes of the previous UNFCCC in Copenhagen.